Embedded Heat Pipe In A Hybrid Cooling System

ABSTRACT

One embodiment of a system for cooling a heat-generating device includes a base adapted to be coupled to the heat-generating device, a housing coupled to the base, a liquid channel formed between the base and the housing, where a heat transfer liquid may be circulated through the liquid channel to remove heat generated by the heat-generated device, and a heat pipe disposed within the liquid channel, where the heat pipe increases the heat transfer surface area to which the heat transfer liquid is exposed. Among other things, the heat pipe advantageously increases the heat transfer surface area to which the heat transfer liquid is exposed and efficiently spreads the heat generated by the heat-generating device over that heat transfer surface area. The result is enhanced heat transfer through the liquid channel relative to prior art cooling systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/294,825 entitled, “EMBEDDED HEAT PIPE IN A HYBRID COOLING SYSTEM,”filed Dec. 5, 2005 and having Attorney Docket No. NVDA/P002015. Thesubject matter of this related application is hereby incorporated hereinby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to systems used to cool computerhardware and more particularly to an embedded heat pipe in a hybridcooling system.

2. Description of the Background Art

FIG. 1 is an isometric view illustrating a prior art cooling system 100used to cool heat-generating electronic devices in a computer system,such as a graphics processing unit (GPU). As shown, cooling system 100characteristically includes a blower/fan 106, fins 109 and a bottomplate 111. Typically, cooling system 100 is thermally coupled to theGPU, for example using thermal adhesive or grease having thermalproperties that facilitate transferring heat generated by the GPU to thebottom plate 111. Cooling system 100 may also include a heat sink lid(not shown), which, among other things, prevents particles and othercontaminants from entering blower/fan 106 and air blown from blower/fan106 from escaping cooling system 100. The heat sink lid, together withthe fins 109 and the bottom plate 111, define a plurality of airchannels 108.

Blower/fan 106 is configured to force air through air channels 108 overbottom plate 111 such that the heat generated by the GPU transfers tothe air. The heated air then exits cooling system 100, as depicted byflow lines 114, thereby dissipating the heat generated by the GPU intothe external environment. This process cools the GPU, preventing thedevice from overheating during operation. Persons skilled in the artwill understand that air channels 108 typically are configured to directair blown from blower/fan 106 over bottom plate 111 and into theexternal environment in a manner that most efficiently removes heat fromthe GPU.

FIG. 2 is a schematic diagram illustrating a computer system 200, suchas a desktop, laptop, server, mainframe, set-top box, and the likewithin which a conventional cooling system 100 for cooling the GPU 216is incorporated. As shown, computing device 200 includes a housing 201,within which a motherboard 204 resides. Mounted on motherboard 204 are acentral processing unit (CPU) 206, a processor cooler 208 for coolingCPU 206, a system fan 210 for removing heat from computing device 200and one or more peripheral component interface (PCI) cards 212, eachinterfaced with a slot located in the back part of housing 201.Motherboard 204 further incorporates a graphics card 202 that enablescomputing device 200 to rapidly process graphics related data forgraphics intensive applications such as gaming applications. Graphicscard 202 comprises a printed circuit board (PCB) upon which a pluralityof circuit components (not shown), such as memory chips and the like,are mounted. In addition, graphics card 200 includes GPU 216, mounted toone face of graphics card 202, for processing graphics related data.

Because the computational requirements of GPU 216 are typically quitesubstantial, GPU 216 tends to generate a large amount of heat duringoperation. If the generated heat is not properly dissipated, theperformance of GPU 216 degrades. For this reason, cooling system 100,which is configured to remove heat from GPU 216, is coupled to GPU 216.

One drawback of these conventional blower/fan cooling systems is that,as processors become more powerful and generate more heat, the fan hasto be operated at very high speeds to generate the airflow through theair channels and over the heat sink necessary to cool the processor.High speed operation tends to produce a substantial amount of unwantedacoustic noise, which is annoying to users of a computer. Also, in someinstances, these types of conventional cooling systems may not even beable to meet the heat dissipation requirements of certainhigh-performance processors. Further compounding these issues is thefact that, while processors are becoming more powerful, the availablespace for cooling systems within computing devices is generally notincreasing. Thus, substantial improvements in the efficiency of coolingsystems are required to maintain pace with the evolution of processors.

Liquid cooling systems are beginning to emerge as a viable alternativeto conventional blower/fan cooling systems. A liquid cooling systemdissipates heat at a much greater rate than a comparable air coolingsystem. However, typical liquid cooling systems are driven by largepumps, which are prone to frequent failure and tend to consume a greatdeal of power. Moreover, such systems tend to use large quantities ofliquid, circulating at a high flow rate, and therefore must befrequently replenished or replaced.

To overcome some of these challenges, a hybrid cooling system isdisclosed in U.S. patent application Ser. No. 10/822,958, filed on Apr.12, 2004 and titled, “System for Efficiently Cooling a Processor,” whichis herein incorporated by reference. FIG. 3 is an isometric view of sucha hybrid cooling system 300. Similar to the system 100, the hybridcooling system 300 may be adapted for use in any type of appropriatecomputing device. As shown, hybrid cooling system 300 may include,without limitation, a fansink 302 and a hybrid cooling module 304. Asdescribed in further detail below, fansink 302 and hybrid cooling module304 may operate independently or in combination to dissipate heat from aprocessor or other heat-generating device within the computer system.

Fansink 302 is configured in a manner similar to cooling system 100 ofFIG. 1 and includes, without limitation, a fan 308, walls 306 and abottom plate 318. Cooling system 300 also includes a heat sink lid 320,which, among other things, prevents particles and other contaminantsfrom entering fan 308 and air blown from fan 308 from escaping system300. Heat sink lid 320, together with walls 306 and bottom plate 318 offansink 302, define a plurality of air channels 322.

Hybrid cooling module 304 is adapted to be integrated with fansink 302.Hybrid cooling module 304 is thermally coupled to a portion of bottomplate 318 and includes, without limitation, a liquid channel 312, aninlet 314, an outlet 316 and a plurality of air channels 310. Hybridcooling module 304 is coupled to a pump, which is adapted forcirculating a heat transfer liquid (e.g., water or any other liquidsuitable for transferring heat) through a closed loop that includesliquid channel 312. As shown in FIG. 3, the pump circulates liquid fromhybrid cooling module 304 through a heat exchanger prior to supplyingthe liquid back to hybrid cooling module 304. Inlet 314 and outlet 316are configured for respectively supplying and removing the heat transferliquid to liquid channel 312. Air channels 310 are adapted for couplingto air channels 322 and for transporting forced air from fan 308 to thelocal environment. Air channels 310 are positioned over and aroundliquid channel 312 such that liquid channel 312 is substantiallyenclosed within air channels 310.

When cooling a processor or other heat-generating device, fan 308 forcesair through air channels 322 of the fansink 302 and air channels 310 ofthe hybrid cooling module 304 such that the heat generated by theprocessor transfers to the air as the air passes over bottom plate 318.The heated air then exits system 300, as depicted by flow lines 324,thereby dissipating the heat generated by the processor into the localenvironment. In addition, as previously described, the pump circulatesthe heat transfer liquid through liquid channel 312 of hybrid coolingmodule 304, and heat generated by the processor transfers to thecirculating heat transfer liquid as well as to air in air channels 310.Liquid channel 312 is adapted for transporting heat transfer liquidthrough a downstream heat exchanger, which dissipates heat from the heattransfer liquid into the local environment.

Fansink 302 and hybrid cooling module 304 may be implementedindependently or in combination to dissipate heat from a processor, inorder to dissipate heat from the processor in the most efficient manner.For example, fansink 302 may be implemented to dissipate a majority ofthe generated heat, hybrid liquid cooling module 304 may be implementedto dissipate a smaller quantity of heat, and the proportions of heatdissipated by fansink 302 and hybrid cooling module 304 may bedynamically adjusted. Alternatively, one of fansink 302 and hybridcooling module 304 may be implemented as a primary means for heatdissipation, while the other mechanism is implemented on an as-neededbasis to dissipate excess heat.

One drawback to using the hybrid cooling system 300 is that, when thepump is inoperative and no heat transfer liquid is circulated throughthe liquid channel 312, a substantial amount of cooling capacity is lostbecause air cooling provided by the fansink 302 is limited to the airchannels 310, 322 that are not obstructed by the liquid channel 312. Inother hybrid cooling system configurations, the fansink and the liquidcooling module may be “stacked” such that the fansink is disposed on topof the hybrid cooling module. In such configurations, when the pump isinoperative and no heat transfer liquid is circulated through the liquidchannel, the standing liquid in the liquid channel acts like aninsulator and retards the heat transfer between the processor or otherheat-generating device and the walls of the fansink air channels,substantially decreasing the cooling efficiency of the hybrid coolingsystem. In addition, when such a “stacked” hybrid cooling system isinstalled in a peripheral component interconnect (PCI) slot, heightrestrictions become a concern. Consequently, the height of the fansinkair channels may be reduced to allow the system to fit within theallocated space. Reducing the height of the air channels reduces theeffective heat transfer area of the air channels, further decreasing thecooling efficiency of the hybrid cooling system.

As the foregoing illustrates, what is needed in the art is a way toincrease the efficiency of hybrid cooling systems, especially when theliquid cooling portion of the system is not being used.

SUMMARY OF THE INVENTION

One embodiment of a system for cooling a heat-generating device includesa base adapted to be coupled to the heat-generating device; a housingcoupled to the base; a liquid channel formed between the base and thehousing, wherein a heat transfer liquid may be circulated through theliquid channel to remove heat generated by the heat-generated device;and a heat pipe disposed within the liquid channel, wherein the heatpipe increases the heat transfer surface area to which the heat transferliquid is exposed. Among other things, the heat pipe advantageouslyincreases the heat transfer surface area to which the heat transferliquid is exposed and efficiently spreads the heat generated by theheat-generating device over that heat transfer surface area. The resultis enhanced heat transfer through the liquid channel relative to priorart cooling systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view illustrating a prior art system used to coola processor.

FIG. 2 is schematic diagram illustrating a computing device adapted foruse with a system for cooling a processor, according to one embodimentof the present invention.

FIG. 3 is an isometric view illustrating a prior art hybrid coolingsystem for cooling a heat-generating electronic device.

FIGS. 4A-C are various views/schematics of a hybrid cooling system withan embedded heat pipe, according to one embodiment of the presentinvention.

FIG. 5 is an alternative embodiment of the hybrid cooling system ofFIGS. 4A-C, according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 4A is an exploded isometric view of a hybrid cooling system 400,according to one embodiment of the present invention. Hybrid coolingsystem 400 is configured to be thermally and structurally coupled to aprinted circuit board (PCB), such as the graphics card 402 or thegraphics card 202 of FIG. 2, and implemented with a computer system,such as the computer system 200 of FIG. 2. Mounted on a top side, thegraphics card 402 includes GPU 416 (more clearly depicted in FIG. 4C)and other components, such as memory units (not shown) and a powersupply (not shown). Preferably, the graphics card 402 is configured toconnect to a computer system via a standard peripheral componentinterconnect PCI slot. Further, the hybrid cooling system 400 isconfigured so that when it is mounted to the graphics card 402, thecooling system 400 and the graphics card 402 will fit substantiallywithin one standard PCI slot of a computer system. In alternateembodiments, the hybrid cooling system 400 may be configured to becoupled to any type of PCB for use in cooling a heat-generatingelectronic device mounted on that circuit board, such as an acceleratedgraphics port (AGP) card.

The hybrid cooling system 400 includes, without limitation, a base 405,a lid 410, a fan 415, a hybrid cooling module 420, a heat pipe 425, aheat sink 430, a heat exchanger (as shown in FIG. 3) and a pump (asshown in FIG. 3). The base 405, the hybrid cooling module 420, the heatpipe 425, and the heat sink 430 are made from a thermally conductivematerial, such as aluminum or copper. The lid 410 and the fan 415 may bemade from plastic or any other appropriate material.

A bottom side of the base 405 is thermally coupled to the GPU 416 so asto conduct heat generated by the GPU 416 during operation. The base 405may also be thermally coupled to other heat generating electronicdevices on the graphics card 402, such as memory units and the powersupply, to conduct heat generated by those electronic devices as well.The heat sink 430, also shown in FIG. 4B, is coupled to a top side ofthe base 405 over at least some of the memory units and at least aportion of the GPU 416 to enable heat generated by these devices andtransferred through the base 405 to be transferred to air forced throughair channels within the heat sink 430 by the fan 415. A second heat pipe(not shown) may be disposed beneath the heat sink 430 to improve heatdistribution throughout the heat sink 430. As described in greaterdetail herein, the fan 415 forces air through the air channels 420 e ofthe hybrid cooling module 420 to enable heat generated by the GPU 416 tobe removed and transferred to the local environment.

FIG. 4B is a top view of the hybrid cooling system 400 without the lid410 and having hidden lines to show the embedded heat pipe 425 and theGPU 416. FIG. 4C is a sectional schematic of the hybrid cooling system400. As shown, the hybrid cooling module 420 is coupled to the top sideof the base 405 and is disposed laterally on the base 405 above the GPU416. The hybrid cooling module 420 is mounted on to the base 405 so thata liquid channel 420 d is formed between the base 405 and the hybridcooling module 420. A seal (not shown) is disposed therebetween toprevent leakage of a heat transfer liquid 440 (e.g., water) within theliquid channel 420 d. Alternatively, the hybrid cooling module 420 mayhave its own base, with the liquid channel formed between that base anda top 420 f of the hybrid cooling module 420, and be sealed prior toinstallation on the base 405. The hybrid cooling module 420 includes aliquid inlet 420 a and a liquid outlet 420 b. The inlet 420 a is coupledto an outlet of the pump via tubing (not shown), and the outlet 420 b iscoupled to an inlet of the heat exchanger via tubing (not shown). Thepump and the heat exchanger may be located distally from the graphicscard 402 in the computer chassis 201 or outside of the computer chassis201. A plurality of fins 420 c are formed in the top 420 f of the hybridcooling module 420. The fins 420 c and the top 420 f form air channels420 e through the hybrid cooling module 420, which may be covered by thelid 410. In one embodiment, the hybrid cooling module 420 is anintegrated part, but in alternative embodiments, the components of thehybrid cooling module 420, such as the fins 420 c and the top 420 f, maybe separate elements coupled together in some technically feasiblefashion.

The heat pipe 425 is disposed in the liquid channel 420 d. Preferably,the heat pipe 425 is press fit into the liquid channel 420 d to ensuregood contact with the base 405 and the top 420 f of the hybrid coolingmodule 420. The heat pipe 425 may even be press fit to such an extent todeform the heat pipe 425 from an originally circular cross-section to asubstantially oval-shape cross-section, as shown in FIG. 4C, to betterensure coupling between the base 405 and the top 420 f of the hybridcooling module 420. The heat pipe 425 may also be thermally coupled tothe base 405 and the hybrid cooling module 420 with thermal adhesive orsolder. The heat pipe 425 is formed in a substantially “U” shape so thata portion of the heat pipe 425 may substantially extend the length ofeach side of the liquid channel 420 d. Alternatively, the heat pipe 425may be substantially “S” shaped along the longitudinal axis to increasethe contact area with the heat transfer liquid 440. As most clearlyshown in FIG. 4B, the hybrid cooling module 420 is preferably disposedrelative to the GPU 416 so that the curved portion of the heat pipe 425resides above the GPU 416. The outside surface of the heat pipe 425 maybe textured to increase the heat transfer rate from the heat pipe 425 tothe heat transfer liquid 440. The workings of the heat pipe 425 areconventional and well-known by those skilled in the art.

In one embodiment, the heat pipe 425 is a passive heat transfer device,employing two-phase flow to achieve an extremely high thermalconductivity. The heat pipe 425 includes a vapor chamber 424 and a wickstructure 425 w which draws liquid 425 l (e.g. water) to a heat source499 (created by the heat generated by the GPU 416 and transferredthrough the base 405) by the use of capillary forces. The liquid 425 levaporates in the wick 425 w when heated and the resulting vapor 425 vescapes to the vapor chamber 424 of the heat pipe 425 where the vapor425 v is then forced by a resulting pressure gradient to cooler regionsof the heat pipe 425 for condensation. The condensed liquid is thenreturned to the heat source 499 via the capillary action. Further detailon the design and implementation of heat pipes in electronics coolingapplications may be found in an article by Scott D. Garner, P. E.,entitled “Heat Pipes for Electronics Cooling Applications,” available athttp://www.electronics-cooling.com/resources/EC_Articles/Sep96_(—)02.htm,which is incorporated herein by reference.

Operation of the hybrid cooling system 400 will now be described. Heatflow from the GPU 416 and through the hybrid cooling module 420 isdenoted by heat paths 435 a and 435 b. Heat is transferred from the GPU416, through the base 405, and to the heat pipe 425. The heat vaporizesthe liquid 425 l in the wick 425 w. The vapor 425 v is forced away fromthe GPU 416 towards the cooler regions of the heat pipe 425, which areshown in FIG. 4B. As the vapor 425 v travels through the heat pipe 425,heat is transferred through the sides of the heat pipe 425 to the heattransfer liquid 440 circulating within the liquid channel 420 d (whenthe pump is operated), as depicted by heat path 435 b. The heattransferred to the heat transfer liquid 440 is transported to the heatexchanger where it is dissipated into the local environment. Heat isalso transferred through the top of the heat pipe 425 to the top 420 fof the hybrid cooling module 420, as depicted by heat path 435 a. Theheat continues through the top 420 f the fins 420 c, where the heat istransferred to the air being forced through the air channels 420 e bythe fan 415. The heat is subsequently dissipated out into the localenvironment as well. When the pump is inoperative, and no heat transferliquid 440 circulates through the liquid channel 420 d, heat onlytravels along heat path 435 a, as described above.

Disposing the heat pipe 425 in the liquid channel 420 d improves theheat transfer capability of the cooling system 400 relative to thecooling system 300 when the pump is both inactive and active. When thepump is inactive, the heat pipe 425 remains operational, since it is apassive device, and thus provides a direct heat path 435 a between theGPU 416 and the fins 420 c. As such, the heat pipe 425 substantiallyimproves heat transfer through the liquid channel 420 d to the fins 420c versus the prior art hybrid cooling system 300 in which, as previouslydescribed, the non-circulating heat transfer liquid acts as an insulatorand impedes the heat transfer between the GPU and the fansink portion ofthe system. When the pump is active, the sides of the heat pipe 425increase the heat transfer surface area to which the circulating liquid440 is exposed, thereby increasing the rate of heat transfer to the heattransfer liquid via heat path 435 b relative to prior art systems.

In an alternative embodiment, the heat pipe 425 may be added into aliquid channel of a liquid-only cooling system 500, thereby realizingthe benefit of increasing the heat transfer area to the circulating heattransfer liquid 440, as described above. For example, as shown in FIG.5, a housing 520 may be used instead of the hybrid cooling module 420,with a liquid channel 420 d defined between the top portion of thehousing 520 and the base 405. The heat pipe 425 is embedded in theliquid channel 420 d, as previously described herein. Again, inoperation, heat is transferred from the GPU 416, through the base 405,and to the heat pipe 425. The heat vaporizes the liquid 425 l in thewick 425 w. The vapor 425 v is forced away from the GPU 416 towards thecooler regions of the heat pipe 425. As the vapor 425 v travels throughthe heat pipe 425, heat is transferred through the sides of the heatpipe 425 to the heat transfer liquid 440 circulating within the liquidchannel 420 d, as depicted by heat path 435 b.

In another alternative embodiment, the hybrid cooling system may beconfigured to be coupled to heat-generating electronic devices otherthan a GPU, such as a central processing unit (CPU), anapplication-specific integrated circuit (ASIC), another type of specialpurpose processing unit, memory elements and the like.

Although the invention has been described above with reference tospecific embodiments, persons skilled in the art will understand thatvarious modifications and changes may be made thereto without departingfrom the broader spirit and scope of the invention as set forth in theappended claims. The foregoing description and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

1. A system for cooling a heat-generating device, the system comprising:a base, having a first side that is thermally coupled to theheat-generating device; a housing coupled to a second side of the base;a liquid channel formed between the base and the housing, wherein a heattransfer liquid may be circulated through the liquid channel to removeheat generated by the heat-generating device; and a heat pipe disposedwithin the liquid channel, wherein the heat pipe is thermally coupled tothe second side of the base and has a first portion proximate to theheat-generating device and second portions extending beyond theheat-generating device to define low-temperature heat pipe regions, theheat pipe being configured to increase the heat transfer surface area towhich the heat transfer liquid is exposed.
 2. The system of claim 1wherein the heat pipe includes a wick structure internal to the surfaceof the heat pipe for drawing liquid to the heat source through capillaryattractors and a vapor chamber within the wick structure and central tothe heat pipe for carrying heated vapor to the cold regions of the heatpipe by a pressure gradient, the cooled liquid thereafter being returnedto the region adjacent the heat generating device.
 3. The system ofclaim 2, further comprising a plurality of fins coupled to a first sideof the housing, wherein a second side of the housing forms a portion ofthe liquid channel.
 4. The system of claim 3, wherein the plurality offins and the housing form an integrated part.
 5. The system of claim 3,further comprising a fan configured to force air through air channelsdefined between the fins.
 6. The system of claim 1, wherein heat istransferred from the heat-generating device to the heat pipe throughconduction, and heat is transferred from the heat pipe to the heattransfer liquid through convection via the heat transfer surface area ofthe heat pipe.
 7. The system of claim 2, wherein an outer surface of theheat pipe is textured.
 8. The system of claim 1, wherein theheat-generating device is a graphics processing unit.
 9. The system ofclaim 8, wherein the graphics processing unit is disposed on a graphicscard, and the system is configured to fit within one standard peripheralcomponent interconnect slot.
 10. The system of claim 1, wherein theheat-generating device is a central processing unit, anapplication-specific integrated circuit or a memory device.
 11. Acomputer system configured with a cooling system, the computer systemcomprising: a base, having a first side that is thermally coupled to theheat-generating device; a housing coupled to a second side of the base;a liquid channel formed between the base and the housing, wherein a heattransfer liquid may be circulated through the liquid channel to removeheat generated by the heat-generating device; and a heat pipe disposedwithin the liquid channel, wherein the heat pipe is thermally coupled tothe second side of the base and has a first portion proximate to theheat-generating device and second portions extending beyond theheat-generating device to define low-temperature heat pipe regions, theheat pipe being configured to increase the heat transfer surface area towhich the heat transfer liquid is exposed.
 12. The computer system ofclaim 11 wherein the heat pipe includes a wick structure internal to thesurface of the heat pipe for drawing liquid to the heat source throughcapillary attractors and a vapor chamber within the wick structure andcentral to the heat pipe for carrying heated vapor to the cold regionsof the heat pipe by a pressure gradient, the cooled liquid thereafterbeing returned to the region adjacent the heat generating device. 13.The computer system of claim 12, further comprising a plurality of finscoupled to a first side of the housing, wherein a second side of thehousing forms a portion of the liquid channel.
 14. The computer systemof claim 13, wherein the plurality of fins and the housing form anintegrated part.
 15. The computer system of claim 13, further comprisinga fan configured to force air through air channels defined between thefins.
 16. The computer system of claim 11, wherein heat is transferredfrom the heat-generating device to the heat pipe through conduction, andheat is transferred from the heat pipe to the heat transfer liquidthrough convection via the heat transfer surface area of the heat pipe.17. The computer system of claim 12, wherein an outer surface of theheat pipe is textured.
 18. The computer system of claim 11, wherein theheat-generating device is a graphics processing unit.
 19. The computersystem of claim 18, wherein the graphics processing unit is disposed ona graphics card, and the system is configured to fit within one standardperipheral component interconnect slot.
 20. The computer system of claim11, wherein the heat-generating device is a central processing unit, anapplication-specific integrated circuit or a memory device.